Quantum phase synchronization revealing few-hundred femtosecond coherence in cryptophyte phycoerythrin 545 antenna from exciton–vibrational coupling

Quantum beats lasting a few hundred femtoseconds have been regarded as signatures of quantum energy transfer in photosynthetic antennae. The fragile coherence at room temperature casts doubt on its long-lived feature arising from the electronic coherence. Recently, the long-lived exciton-vibrational coherences of several hundred femtoseconds via quantum phase synchronization of the resonant higher frequency collective vibrational modes have been observed in core antenna allophycocyanin from algae. The long-lived coherence has an inherent property of protecting the coherence against the noisy environment. This is achieved by dissipation of the resonant anti-symmetric collective vibrational modes coupled to the excitonic levels, which have fast dephasing, leaving only the non-dissipative correlated symmetric modes [R. Zhu et al., Nat. Commun. 15, 3171 (2024)], which is different from that induced by the environmental low frequency modes. Coherence with a lifetime constant of 200 fs at room temperature has been observed in the cryptophyte phycoerythrin 545 (PE545) antenna before, while its origin, i.e., pure electronic or exciton-vibrational, remains to be explored. Here, we investigated coherent energy transfer dynamics in PE545 via two-dimensional electronic spectroscopy. A long-lasting coherence with a lifetime constant of 270 fs in the dynamical Stokes shift dynamics was observed. Especially, the high frequency vibrational mode at 1150 cm-1 is absent in the electronic energy dissipation process reflected in the dynamical Stokes' shifts spectrum, which is near resonant with the electronic gap of 1080 cm-1. Therefore, the facts strongly suggest that the long-lived coherence in PE545 is realized by the resonant exciton-vibrational coupling via quantum phase synchronization.